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Title: Effects of subduction parameters on geothermal gradients in forearcs with an application to Franciscan subduction in California

Abstract

Geothermal gradients in forearcs are often suppressed below normal values because of the cooling effect of the relatively cold downgoing plate. In this paper, finite difference thermal modeling is used to evaluate the influence on forearc gradients of variations in six potentially important subduction zone parameters: radiogenic heat production; thermal conductivity of forearc rocks; subduction angle; subduction rate; frictional heat production; and presubduction geothermal gradients. Pressure-temperature conditions of blueschist-facies metamorphism in the Franciscan subduction complex of California are easily explained with typical subduction rates and slab ages with plate contact shear stresses of the order of 10 MPa, but stresses within the range zero to a few tens of megapascals are probably permitted by the thermal constraints. Speculative application of the modeling results assuming a shear stress of 4% of lithostatic pressure to plate motion reconstructions for the Franciscan forearc suggests that forearc gradients were about 8C/km around 85 Ma when the subducting slab was perhaps 145 m.y. old and the subduction rate was perhaps 95 km/m.y. Gradients increased moderately through the latest Cretaceous to middle Tertiary as subduction became slower and the subducting slab became younger, reaching about 16C/km at 28 Ma when the slab age was about 11more » m.y. and the subduction rate was about 48 km/m.y. The slab age, subduction rate, and forearc gradient then remained fairly constant until 5 Ma, when subduction slowed to about 32 km/m.y. and the slab age decreased to about 8 m.y., causing gradients to rise to about 20C/km.« less

Authors:
 [1]
  1. La Trobe Univ., Bundoora, Victoria (Australia)
Publication Date:
OSTI Identifier:
5589805
Resource Type:
Journal Article
Journal Name:
Journal of Geophysical Research; (United States)
Additional Journal Information:
Journal Volume: 96:B1; Journal ID: ISSN 0148-0227
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CALIFORNIA; SUBDUCTION ZONES; GEOTHERMAL GRADIENTS; AGE ESTIMATION; COOLING; CRETACEOUS PERIOD; FINITE DIFFERENCE METHOD; FRICTION; GEOLOGIC HISTORY; INCLINATION; MASS TRANSFER; MATHEMATICAL MODELS; METAMORPHISM; PLATE TECTONICS; RADIOACTIVITY; RESERVOIR PRESSURE; RESERVOIR ROCK; RESERVOIR TEMPERATURE; SHEAR; TERTIARY PERIOD; THERMAL CONDUCTIVITY; CENOZOIC ERA; DEVELOPED COUNTRIES; FEDERAL REGION IX; GEOLOGIC AGES; ITERATIVE METHODS; MESOZOIC ERA; NORTH AMERICA; NUMERICAL SOLUTION; PHYSICAL PROPERTIES; TECTONICS; TEMPERATURE GRADIENTS; THERMODYNAMIC PROPERTIES; USA; 580000* - Geosciences

Citation Formats

Dumitru, T A. Effects of subduction parameters on geothermal gradients in forearcs with an application to Franciscan subduction in California. United States: N. p., 1991. Web. doi:10.1029/90JB01913.
Dumitru, T A. Effects of subduction parameters on geothermal gradients in forearcs with an application to Franciscan subduction in California. United States. doi:10.1029/90JB01913.
Dumitru, T A. Thu . "Effects of subduction parameters on geothermal gradients in forearcs with an application to Franciscan subduction in California". United States. doi:10.1029/90JB01913.
@article{osti_5589805,
title = {Effects of subduction parameters on geothermal gradients in forearcs with an application to Franciscan subduction in California},
author = {Dumitru, T A},
abstractNote = {Geothermal gradients in forearcs are often suppressed below normal values because of the cooling effect of the relatively cold downgoing plate. In this paper, finite difference thermal modeling is used to evaluate the influence on forearc gradients of variations in six potentially important subduction zone parameters: radiogenic heat production; thermal conductivity of forearc rocks; subduction angle; subduction rate; frictional heat production; and presubduction geothermal gradients. Pressure-temperature conditions of blueschist-facies metamorphism in the Franciscan subduction complex of California are easily explained with typical subduction rates and slab ages with plate contact shear stresses of the order of 10 MPa, but stresses within the range zero to a few tens of megapascals are probably permitted by the thermal constraints. Speculative application of the modeling results assuming a shear stress of 4% of lithostatic pressure to plate motion reconstructions for the Franciscan forearc suggests that forearc gradients were about 8C/km around 85 Ma when the subducting slab was perhaps 145 m.y. old and the subduction rate was perhaps 95 km/m.y. Gradients increased moderately through the latest Cretaceous to middle Tertiary as subduction became slower and the subducting slab became younger, reaching about 16C/km at 28 Ma when the slab age was about 11 m.y. and the subduction rate was about 48 km/m.y. The slab age, subduction rate, and forearc gradient then remained fairly constant until 5 Ma, when subduction slowed to about 32 km/m.y. and the slab age decreased to about 8 m.y., causing gradients to rise to about 20C/km.},
doi = {10.1029/90JB01913},
journal = {Journal of Geophysical Research; (United States)},
issn = {0148-0227},
number = ,
volume = 96:B1,
place = {United States},
year = {1991},
month = {1}
}